The demand for renewable load-carrying materials is increasing with increasing environmental awareness. Alternative sources for materials manufacturing and design have to be investigated in order to replace the non-biodegradable materials. The work presented in this thesis investigates structure-property relations of such renewable materials based on cellulose nanofibrils. Cellulose is the most abundant polymer on earth and exists in both ordered and disordered phases, where the ordered crystalline cellulose shows excellent mechanical properties. The celluloses nanofibril is composed of partly crystalline cellulose where the stiff crystal regions, or crystallites, are orientated in the axial direction of the fibrils. The cellulose nanofibrils have a high aspect ratio, i.e. length to diameter ratio, with a diameter of less than 100 nm and a length of some micrometres. In the presented work, different properties of the cellulose nanofibril were studied, e.g. elastic properties, structure, and its potential as a reinforcement constituent. The properties and behaviour of the fibrils were studied with respect to different length scales, from the internal structure of the cellulose nanofibril, based on molecular dynamic simulations, to the macroscopic properties of cellulose nanofibril based materials. Films and composite materials with in-plane randomly oriented fibrils were produced. Properties of the cellulose nanofibril based materials, such as stiffness, thickness variation, and fibril orientation distribution, were investigated, from which the effective elastic properties of the fibrils were determined. The studies showed that a typical softwood based cellulose nanofibril has an axial stiffness of around 65 GPa. The properties of the cellulose nanofibril based materials are highly affected by the dispersion and orientation of the fibrils. To use the full potential of the stiff fibrils, well dispersed and oriented fibrils are essential. The orientation distribution of fibrils in hydrogels subjected to a strain was therefore investigated. The study showed that the cellulose nanofibrils have high ability to align, where the alignment increased with increased applied strain.

In this thesis the orientation of macro-sized fibres in turbulent flows is studied, as well as the effect of nano-sized fibrils on hydrodynamic stability. The focus lies on enabling processes for new materials where cellulose is the main constituent. When fibres (or any elongated particles) are added to a fluid, the complexity of the flow-problem increases. The fluid flow will influence the rotation of the fibres, and therefore also effect the overall fibre orientation. Exactly how the fibres rotate depends to a large extent on the mean velocity gradient in the flow. In addition, when fibres are added to a suspending fluid, the total stress in the suspension will increase, resulting in an increased apparent viscosity. The increase in stress is related to the direction of deformation in relation to the orientation of the particle, i.e. whether the deformation happens along the long or short axis of the fibre. The increase in stress, which in most cases is not constant neither in time nor space, will in turn influence the flow. This thesis starts off with the orientation and spatial distribution of fibres in the turbulent flow down an inclined plate. By varying fibre and flow parameters it is discovered that the main parameter controlling the orientation distribution is the aspect ratio of the fibres, with only minor influences from the other parameters. Moreover, the fibres are found to agglomerate into streamwise streaks. A new method to quantify this agglomeration is developed, taking care of the problems that arise due to the low concentration in the experiments. It is found that streakiness, i.e. the tendency to agglomerate in streaks, varies with Reynolds number. Going from fibre orientation to flow dynamics of fibre suspensions, the influence of cellulose nanofibrils (CNF) on laminar/turbulent transition is investigated in three different setups, namely plane channel flow, curved-rotating channel flow, and the flow in a flow focusing device. This last flow case is selected since it is can be used for assembly of CNF based materials. In the plane channel flow, the addition of CNF delays the transition more than predicted from measured viscosities while in the curved-rotating channel the opposite effect is discovered. This is qualitatively confirmed by linear stability analyses. Moreover, a transient growth analysis in the plane channel reveals an increase in streamwise wavenumber with increasing concentration of CNF. In the flow focusing device, i.e. at the intersection of three inlets and one outlet, the transition is found to mainly depend on the Reynolds number of the side flow. Recirculation zones forming downstream of two sharp corners are hypothesised to be the cause of the transition. With that in mind, the two corners are given a larger radius in an attempt to stabilise the flow. However, if anything, the flow seems to become unstable at a smaller Reynolds number, indicating that the separation bubble is not the sole cause of the transition. The choice of fluid in the core flow is found to have no effect on the stability, neither when using fluids with different viscosities nor when a non-Newtonian CNF dispersion was used. Thus, Newtonian model fluids can be used when studying the flow dynamics in this type of device. As a proof of concept, a flow focusing device is used to produce a continuous film from CNF. The fibrils are believed to be aligned due to the extensional flow created in the setup, resulting in a transparent film, with an estimated thickness of 1 um. / <p>QC 20141003</p>

Ce projet s’est focalisé sur l’ajout de nouvelles propriétés à des papiers grâce à l’utilisation de nanocelluloses fonctionnelles. Ces nanocelluloses sont des nanoparticules extraites du bois qui peuvent être divisées en deux catégories : les nanofibrilles de cellulose (CNFs) et les nanocristaux de cellulose (CNCs). Ce travail s’est essentiellement penché sur l’utilisation des CNFs. Leur réactivité chimique a été utilisée afin de les fonctionnaliser avec des organotrialkoxysilanes. C’est aussi leur fort enchevêtrement ainsi que la grande viscosité de ces CNFs en suspension qui ont été utilisés afin de synthétiser des petites particules de silsesquioxane pour rendre le matériau final antimicrobien et (super)hydrophobe. Les connaissances obtenues à travers l’étude sur des films modèle de CNFs ont ensuite été appliquées au couchage du papier. Ces CNFs fonctionnelles ont donc été évaluées pour le développement d’un papier possédant une surface antimicrobienne, anti-adhérente, barrière aux graisses ou superhydrophobe. / The aim of this work is to implement new properties to a paper based material via the use of functional nanocelluloses. Nanocelluloses are nanoparticles extracted from wood and distinguished in two categories: Cellulose Nanofibrils (CNFs) and Cellulose Nanocrystals (CNCs). This work has only been carried out with CNFs. The chemical reactivity of CNFs was used to functionalize them with organotrialkoxysilanes. The entangled network and highly viscous suspension of CNFs was also used to synthesize silsesquioxane particles with limited size to impart (super)hydrophobic and antimicrobial properties. Knowledge obtained through the study of model CNFs films was then applied to paper based material coating. The functional CNFs were evaluated for its use in an antimicrobial, anti-adherent, greaseproof or superhydrophobic paper surface.

CO2 adsorption is considered as a promising strategy to decrease the amount of CO2 in the atmosphere and stop global warming. The goal of this project is to prepare a cellulose-based CO2 adsorbent with a good mass transfer. Monolithic adsorbent based on cellulose nanofibrils (CNF) was fabricated via freeze-casting. 0.1g or 0.5g cellulose acetate (CA) or 0.1g acetylated CNC (aCNC) was dipped into the crosslinked aerogel to increase its CO2 capacity. Acetylation of CNC was confirmed by Fourier transformed infrared spectroscopy (FT-IR) and the degree of substitution was determined to be 1.6 through titration. Scanning electron microscopy (SEM) images showed that monolithic structure was formed through freeze-casting and the structure was maintained after dipping. Compression test suggested that the mechanical properties of the aerogel increased with the increasing amount of dipped CA, while the CO2 capacity of the adsorbent decreased. Furthermore, the outstanding reinforcing effect of aCNC was noticed in the compression test, and the aerogel dipped with aCNC has the highest CO2 capacity with a value of 1.49 mmol/g.

Cellulose nanofibrils are a biobased and renewable material with potential to be used in many different applications. Such applications include air filtration, absorption of liquids, and thermal insulation.  To be used for these applications the cellulose nanofibrils must form a porous and dry material. However, maintaining some degree of porosity after drying is difficult, since the fibrils are extracted in liquid and tend to collapse into a dense material upon drying. Certain methods have proven effective for making a dry porous material from cellulose nanofibrils, but these are often expensive and not suitable for large scale production. The aim of this project is to test possible methods for making a highly porous cellulose nanofibril-based material. These methods must be environmentally sustainable and suitable for large scale production. An extensive screening has been conducted with the aim of identifying methods resulting in materials with high porosity. The obtained materials have been analysed further to give a more thorough understanding of the porosity as well as other characteristics. The results indicate that cross-links in the material strengthen the structure, and that drying samples from water always results in complete collapse or very dense materials while drying samples from certain solvents other than water results in more porous materials. The analysed materials had very different porosities, some of which were relatively high. The most porous material analysed by Brunauer-Emmett-Teller gas adsorption had a surface area of 9.5 m2/g. This project gives insight into how cross-linking chemistries and treatment with different solvents and pH affect the resulting cellulose nanofibril-based material, as well as knowledge about which methods can be used to successfully produce dry porous cellulose nanofibril-based materials.

Nanoparticles are very interesting components. Due to their very large specific surface area they possess properties in between molecules and macroscopic materials. In addition, a material built up of hierarchically assembled nanoparticles could obtain unique properties, not possessed by the nanoparticles themself. A very interesting group of nanoparticles is the cellulose nanofibrils. The fibrils are found in various renewable resources such as wood, bacteria and tunicates. In this work fibrils extracted from wood is studied. In wood the fibrils are the smallest fibrous component with the approximate dimensions; 4 nm in width and length in the micrometer range, providing a high aspect ratio. In addition, they have a crystallinity above 60% and, hence, a high stiffness. These fibrils are hierarchically ordered in the wood fiber to give it its unique combination of flexibility and strength. The properties of the fibrils make them very suitable to be used as reinforcement elements in composites and, due to their ability to closely pack, to make films with excellent gas barrier properties. The key aspect to design materials, efficiently utilizing the properties of the individual fibrils, is to control the arrangement of the fibrils in the final material. In order to do so, the interactions between fibrils have to be well characterized and controlled. In this thesis the interaction between fibrils in aqueous dispersions is studied, where the main interactions are attractive van der Waals forces and repulsive electrostatic forces. The electrostatic forces arise from carboxyl groups at the fibrils surface, which either are due to hemicelluloses at the fibrils surfaces or chemically introduced to the cellulose chain. This force is sensitive to the chemical environment. It decreases if the pH is reduced or if the salt concentration is increased. If it is strongly reduced the system aggregates. In dilute dispersions aggregation causes formation of multiple clusters, whereas in semi-dilute dispersions (above the overlap concentration) a volume filling network, i.e. a gel, is formed. The tendency of aggregation, i.e. the colloidal stability, can be predicted by using the DLVO theory. In this thesis DLVO predictions are compared to aggregation measurements conducted with dynamic light scattering. Good agreement between experiments and the designed theoretical model was found by including specific interactions between added counter-ions and the carboxyl groups of the fibrils in the model. Thus, the surface charge is both reduced by protonation and by specific interactions. This emphasizes a much larger effect of the counter-ions on the stability then generally thought. Hence, this work significantly improves the understanding of the interfibril interactions in aqueous media. As mentioned above, the fibrils can be physically cross-linked to form a gel. The gelation is an instant process, occurring at pH or salt levels causing the interfibril repulsion to decrease close to zero. If a well dispersed stationary dispersion is gelled, the homogenous and random distribution of the fibrils is preserved in the gel. These gels can be used as templates to produce composites by allowing monomers or polymers to enter the network by diffusion. In an effort to mimic processes occurring in the tree, producing materials with fibrils aligned in a preferred direction, the ability to form gels with controlled fibril orientation were studied. Such networks were successfully produced by applying strain to the system prior or past gelation. Orientation prior gelation was obtained by subjecting the dispersion to elongational flow and freezing the orientation by “turning off” the electrostatic repulsion. Orienting the fibrils after gelation was achieved by applying shear strain. Due to the physical nature of the crosslinks, rotation in the fibril-fibril joints can occur, enabling the fibrils to align in the shear direction. This alignment significantly increased the stiffness of the gels in the shear direction. / QC 20111205

<p> Cellulose-based materials have been attracting significant attention in recent years for their potential as renewable and biodegradable materials. Cellulose nanofibrils (CNFs) in particular are readily attainable from woody biomass in high purity and without harsh chemical processes. These CNFs can undergo chemical surface modifications after a simple workup, imbuing them with new attributes that differ from their naturally paper-like structure and properties. In this research, CNFs are modified with oleic acid—another common biomass found in high concentrations in some vegetable oils—which transforms the naturally hydrophilic cellulose into a superhydrophobic material. This transformation can be carried out using solventless mechanochemistry and worked up in ethanol, supporting a green process from start to finish.</p> <p><br></p> <p>Since cellulose contains many free, exposed hydroxyl groups, carboxylic acids can be condensed onto exposed hydroxyls to form esters. In this research, we focus specifically on the oleic acid moiety because its internal alkene has potential for further reactivity. Here we explore methods to introduce crosslinks into esterified CNF (eCNF) for structural and mechanical reinforcement between fibrils. Several methods are attempted, including methods involving thiolene chemistry and epoxide ring opening.</p> <p><br></p> <p>Additionally, efforts have been made to develop a method to disperse eCNF materials in ethyl acetate for deposition by spray coating. Dispersions of eCNF in ethyl acetate are sufficiently stable to enable deposition using simple airbrushing tools. The eCNF coatings are homogenous, superhydrophobic, and have good adhesion to a wide variety of surfaces. </p>

Today, paper and paperboard is an important part of the packaging industry, as well as natural part of our daily lives. The alternatives to paper and paperboard is often produced from nonrenewable sources such as petroleum and as demands on sustainability increase in the packaging sector, it gives paper a desirable advantage over plastics. To increase the use of paper, some of the limiting factors for paper needs to be overcome, such as its limited formability. One way to create a paper that can be formed in new ways is to imbibe the paper with an additive that makes its modulus changeable. This would make it possible to control the stiffness of the paper which would make it more formable. This have been the aim of this thesis. To create this formable paper four different approaches were used. Of these four, three included how paper can be treated with polyelectrolytes to be able to increase its modulus when stimuli are applied. The two first approaches were based on the layer-by-layer technique adsorbing alginate and cationic fibrils to form a layer that could be cross-linked, either on the surface of a film (the first approach) or in the network of fibres in a porous paper (the second approach). The last approach was to impregnate the papers with alginate. The results show that the first approach gave a too low adsorption of polyelectrolytes, why no difference could be detected. The second approach resulted in a higher adsorbed amount, but the effects were still too small. The third approach gave a paper which could, depending on the concentration of alginate, either increase or decrease its modulus when cross-linked. The last approach was to create a laminate, using unmodified fibers together with dialcohol cellulose fibres. This resulted in a paper that could be formed using heat and allowing the paper to cool down in the desirable form. In the curriculum for chemistry in Swedish high schools there is a paragraph that says that research in chemistry should be a part of the content the students learn. This is a challenge both to teachers and researchers. For teachers, to find research at an appropriate level and teach it in an understandable way. For researchers, to communicate the research so it is understandable for society. With this as a motivation, a second part of this thesis discuss the method flipped classroom in chemistry education at Swedish high schools. It was seen that from the teacher’s perspective, flipped classroom meant advantages that could be categorized into five categories. The categories that was found were Time to interact, Student responsibility, dialogue, laboratory work and understanding and using the language. / Pappers- och kartongindustrin är idag en viktig del av förpackningsindustrin. Alternativ till kartong är ofta producerat av icke-förnybara råvaror och idag när kraven på hållbarhet ökar ger detta kartong en fördel mot plast. För att öka användningsområdena för kartong så måste de begränsningar som materialet har idag övervinnas. Detta gäller till exempel formbarheten. Ett sätt att skapa kartong som kan bli format på nya sätt är att göra en additiv tillsats till papperet som har egenskapen att det kan variera sin styvhet. Detta skulle göra det möjligt att kontrollera papperets styvhet, vilket har varit målet för det här arbetet. Genom att använda fyra olika arbetssätt har denna egenskap försökts åstadkommas. Tre av arbetssätten har behandlat papper med polyelektrolyter vars E-modul kan ökas med hjälp av något stimuli. I de två första försöken applicerades polyelektrolyterna genom den så kallade lager-på-lager-tekniken, där alginat och katjoniska cellulosafibriller adsorberades, i första försöket på ytan av en film och i det andra på ytan av fibrerna i fibernätverket i ett poröst papper. I det tredje försöket impregnerades de orösa papperna med alginat. Resultatet från det första försöket var att adsorptionen inte gav någon effekt eftersom den absorberande mängden var för låg. I det andra försöket var adsorptionen högre men det påverkade inte de mekaniska egenskaperna nämnvärt. I det tredje försöket med impregnering så kunde en ändring av E-modulen observeras när systemet tvärbands. I det sista försöket användes en metod som byggde på laminering. Ett ark av modifierade fibrer guskades ihop med ett ark med dialkoholcellulosefibrer. De försök som gjordes tyder på att papperet kunde formas och kunde fås att behålla formen om det värmdes och kyldes i den önskade formen. I läroplanen för kemi på gymnasiet finns en paragraf som beskriver hur kemiundervisningen ska ha inslag av forskning. Detta är en utmaning för både lärare och forskare. Lärarnas utmaning består i att finna forskning på en bra nivå för eleverna och att förklara den på ett förståeligt sätt. För forskare består utmaningen i att kommunicera forskningen på ett förståeligt sätt till samhället. Med detta som motivering har detta arbete en utbildningsdel. I den har lärares perspektiv på metoden ”flipped classroom” i kemiklassrummet undersökts. Flipped classroom beskrevs ha styrkor och dessa kunde kategoriseras i fem kategorier. Kategorierna var tid för interaktion, elevens ansvar, dialog, laborationer och förstå och använda språket.

Active substances can be stabilized to be protected from undesirable reactions, aggregation, and leaking, which would keep the intended functions of the active substances without premature degradation. Among such active substances are paraffin-based organic phase change materials (PCMs) and essential oils (EOs), which feature attractive characteristics, e.g., high latent heat of fusion and inherent antimicrobial activity. However, their high volatility requires an effective stabilization strategy. Petroleum-based synthetic polymers have often been employed to stabilize PCMs and EOs by encapsulation and complexation pathways. Despite their proven effectiveness, these polymers are from non-renewable resources, and non-degradable and often toxic, which has prompted a need to develop a substitute arising from natural polymers that are environmentally benign, biodegradable, and sustainable. Valorization of biomass in this regard would add extra value to biomass otherwise burned or wasted. This dissertation will present the development of microcapsules and inclusion complexes consisting of a hydrophobic active substance core and a polysaccharidic shell originating from biomass. The first two chapters will explain the introduction and experimental details. Chapter 3 will present the microencapsulation of n-hexadecane as PCM via oil-in-water (O/W) Pickering emulsions stabilized by unmodified cellulose nanofibrils (CNFs) through a sonochemical technique. Chapter 4 will investigate the incorporation of the PCM-CNF microcapsules into TEMPO-oxidized CNF films for building application. Finally, Chapter 5 will show the synthesis of EOs-beta cyclodextrin (βCD) inclusion complexes as a guest-host system through a sonochemical technique.

Non-spherical particles are present all around us, in biological, industrial and environmental processes. Making predictions of their impact on us and systems in our vicinity can make life better for everyone here on earth. For example, the ash particles from a volcano eruption are non-spherical and their spreading in the atmosphere can hugely impact the air traffic, as was also proven in 2010. Furthermore, the orientation of the wood fibres in a paper sheet influences the final properties of the paper, and the cause of a specific fibre orientation can be traced back to the fluid flows during the manufacturing process of the paper. In this thesis, experimental and numerical work is presented with the goal to understand and utilize the behavior of elongated particles in fluid flows. Two different experimental setups are used. The first one, a turbulent half channel flow, aims at increasing the understanding of how particles with non-zero inertia behave in turbulence. The second setup is an attempt to design a flow field with the purpose to align nanofibrils and create high performance cellulose filaments. Experiments were performed in a turbulent half channel flow at different flow set- tings with dilute suspensions of cellulose acetate fibres having three different aspect ratios (length to width ratio). The two main results were firstly that the fibres agglom- erated in streamwise streaks, believed to be due to the turbulent velocity structures in the flow. Secondly, the orientation of the fibres was observed to be determined by the aspect ratio and the mean shear, not the turbulence. Short fibres were oriented in the spanwise direction while long fibres were oriented in the streamwise direction. In order to utilize the impressive properties (stiffness comparable to Kevlar) of the cellulose nanofibril in a macroscopic material, the alignment of the fibrils must be controlled. Here, a flow focusing device (resulting in an extensional flow), designed to align the fibrils, is used to create a cellulose filament with aligned fibrils. The principle is based on a separation of the alignment and the assembly of the fibrils, i.e. first align the fibrils and then lock the aligned structure. With this process, continuous filaments were created, with properties similar to that of the wood fibre at the same fibril alignment. However, the highest alignment (lowest angle) of the fibrils in a filament created was only 31o from the filament axis, and the next step is to increase the alignment. This thesis includes modeling of the alignment process with the Smoluchowski equation and a rotary diffusion. Finding a model that correctly describes the alignment process should in the end make it possible to create a filament with fully aligned fibrils. / <p>QC 20140908</p>